The present invention relates to a new and improved method of, and apparatus for, detecting a fault location at an electrical conductor or line from measurement voltages and measurement currents received at a measurement location following an error-indicating excitation signal. This invention also relates to a new and improved construction of apparatus for the preformance of the aforesaid method.
One such localized determination of defects or faults appearing at electrical conductors or lines -- what is generally detected are short-circuits and potential drop faults possessing low to negligible residual voltage at the defect location -- is generally performed with the aid of distance relays. In this regard there are utilized electromechanical or even at the present time electronic analog computer elements, the proper functionality of which requires essentially sinusoidal measurement signals or input signals. However, these measurement signals are only available at the measurement location or station after a certain time following the occurrence of the fault or the arrival of the fault signal, because the transient signals triggered by a short-circuit initially extremely distort the fundamental operating frequency of the conductor and decay comparatively slowly. Therefore it is necessary to resort to either an appropriate time-delay until deriving valid distance results, or to resort to the use of frequency filters which permit of an earlier evaluation of the fundamental frequency components. Both techniques are basically disadvantageous, and specifically, on the one hand owing to the desired rapid control of the protective switch arranged after the distance relay and, on the other hand, because of undesired inertia-prone transition functions of the filter which once again result in a time-delay and, under certain circumstances, can also even have an undesired affect upon the functionality of the relay.
It is therefore desirable to have a fault location-detection which is already functional during the compensation operations following the appearance of the short-circuit and does not require any time-delay interval until the start of its functional operation and as concerns such functional operation only requires as short as possible period of time.
In this connection there are already known to the art fault location-detecting techniques which operate with travelling waves. There is specially generated a test signal possessing a steep wave front which is applied to the conductor or line to be monitored. The re-appearance of the wave reflected by the fault or defect location back to the transmitting or measurement location and the duration of the time interval required for the travel of the test signal to the fault location and back again to the measurement location in conjunction with the known speed of travel of the wave at the conductor determines the distance between the fault location and the measurement location.
What is disadvantageous with this state-of-the-art technique, apart from the need for a special transmitter, is the sensitivity of the system to disturbance signals as such particularly appear with considerable intensity at power current lines and especially high-voltage lines with steep wave flanks. This sensitivity is predicted upon the fact that the detection method basically relies upon a signal flank detection which is based upon a time differential measurement technique. Moreover, the measurement operation becomes critical when the measurement location is situated very near to the fault locations owing to the extremely small travel times.